The subject matter disclosed herein relates to X-ray imaging systems, and more specifically, to X-ray imaging systems utilizing a digital X-ray detector having pixels fabricated with crystalline silicon.
Digital X-ray imaging systems are used to generate digital data in a non-invasive manner and to reconstruct such digital data into useful radiographic images. In current digital X-ray imaging systems, radiation from a source is directed toward a subject or object, typically a patient in a medical diagnostic application, a package or baggage in a security screening application, or a fabricated component in an industrial quality control or inspection application. A portion of the radiation passes through the subject or object and impacts a detector. The scintillator of the detector converts the higher-energy X-ray radiation to lower-energy light photons that are sensed using photo-sensitive components (e.g., photodiodes or other suitable photodetectors). The detector is typically divided into a matrix of discrete picture elements or pixels, and encodes output signals based upon the quantity or intensity of the radiation impacting each pixel region. The signals may then be processed to generate an image that may be displayed for review.
In practice, the detector features may be based on or formed from a silicon semiconductor substrate. Such a silicon substrate may be provided as crystalline silicon (c-Si), which consists of an ordered silicon matrix (e.g., a well ordered crystal lattice), or amorphous silicon (a-Si), which does not have an ordered matrix (e.g., a random crystal lattice). The random crystal lattice of a-Si allows an electron mobility of <1 cm2/(v·s) while the ordered crystal lattice of c-Si allows an electron mobility of approximately 1,400 cm2/(v·s). Because of the higher electron mobility associated with c-Si, the size of features that can be formed using c-Si can be much smaller than those formed from the a-Si, enabling multiple gate active pixel designs with charge amplifier inside the pixel as well as the in-panel readout circuitry including analog to digital converter (A/D).
Thus, in practice, X-ray detectors based on c-Si technology, such as those employing complementary metal-oxide-semiconductors (CMOS) formed from c-Si, have been demonstrated to outperform traditional a-Si based X-ray detector in various ways, including, but not limited to: relative immunity to electromagnetic interference (EMI), reduced electronic noise, reduced image lag, higher spatial resolution, higher frame rate, broader scintillating material selection, and so forth. However, disadvantages of using c-Si include: higher cost, lower dynamic range due to lower voltage swings, and smaller panel size (due to limitations in the practical size of silicon wafers used to fabricate c-Si devices) that may require tiling multiple, smaller panels together to form a larger detector panel. Such tiling arrangements also introduce complexities in the electrical interconnection arrangements needed to operate such a detector panel.